British Pat. No. 1,545,507 discloses that a diphenylimidazole forms a dye upon the oxidation coupling thereof to an aminophenol and that such a diphenylimidazole is useful for forming a coupler for photographic use and such a dye which is formed upon the oxidation coupling of diphenylimidazoles to aminophenols is capable of reproduce an image excellent in light-fastness through a mordant treatment applied thereto with a quaternary ammonium mordant.
However, in the dyes formed through such an oxidation coupling of a diphenylimidazole to an aminophenol, an image color reproduction depends upon pH values. If a pH is neutral, a .lambda. maximum of absorption wavelength is substantially inclined to a short wavelength region. Therefore, it is essential to make a quaternary mordant present whenever such a dye is used so as to reproduce an image.
In such a system not having any of such a mordant present, a .lambda. max of light absorption of these dyes will shift into the green spectral region of the visible light region. Therefore, these dyes cannot be applied as cyan dyes to a variety of image-forming means in color reproduction processes and, more particularly, in color subtraction process which is to be applied to photographic, thermal-transfer, ink-jet, printing and other image forming techniques.
As the result of devoting the inventors themselves in various studies, they have finally achieved this invention upon having found the fact that it is possible to obtain a compound which is suitable to serve as a cyan dye and is less in pH dependence, not necessary for any mordant, capable of displaying more preferably spectral absorption characteristics for a cyan dye and excellent in light-fastness, when a specific paraphenylenediamine compound is used in place of the aforementioned aminophenols.